We propose to use a genetic model system to test the significance of a neuron specific glycoprotein for normal nervous system development. All central nervous system neurons in insects express an antigen that can be recognized by antibodies raised against the heterologous plant glycoprotein horse radish peroxidase (HRP). These antibodies apparently recognize the carbohydrate portion of a neuron specific glycoprotein which is expressed not only by differentiated adult neurons, but also on early embryonic stage neuronal precursor cells. We will purify this HRP-like antigen for Drosophila and produce polyclonal antibodies which can recognize the protein core. The antibodies will be used to isolate a cDNA clone containing the amino acid coding sequence for the antigen. The chromosomal position of the gene coding for the antigen will be mapped by in situ hybridization and various mutants will be constructed to examine the functional role of the antigen during normal nervous system development. These mutants will include deletion mutants constructed by classical genetic crosses of existing stocks and specific site directed mutations, such as amino acid replacement, using oligonucleotide directed mutagenesis. Mutant clones will be reintroduced into developing embryos by P-element mediated transformation and neuronal development will be analyzed both in vivo and in vitro. Our experiments should provide a better understanding of the relationship of specific neuronal phenotypic gene expression in mediating normal nervous system development.